Full duplex transmission, i.e., simultaneous transmission and reception of an electrical signal at both ends of a single transmission line, of digital signals is well known. In the data processing art in which the high frequency transmission of binary digits, i.e., bits, representative of 1's and 0's between modular elements is often required, full duplex transmission is utilized to reduce the number of transmission lines therebetween. In the W. J. Davis U.S. Pat. No. 3,725,582 there is disclosed one prior art transmission line system including a balanced transmission line for the transmission of binary level direct current (DC) signal levels. Such system includes a resistor bridge network of high impedance with respect to the transmission line and terminating resistors for bridge balance with an assumed zero drive impedance. The present invention is considered to be an improvement over such prior art systems.